Updated February 21, 2017 | Factmonster Staff

An avalanche is any swift movement of snow, ice, mud, or rock down a mountainside or slope. Avalanches, which are natural forms of erosion and often seasonal, can reach speeds of more than 200 miles per hour. They are triggered by such events as earthquake tremors, human-made disturbances, or excessive rainfall.

Destruction from avalanches results both from the avalanche wind (the air pushed ahead of the mass) and from the actual impact of the avalanche material.

  • Where: Italian Alps
  • When: 218 B.C.
  • When Hannibal, the Carthaginian general, crossed the Alps to conquer Rome, 18,000 soldiers, 2,000 horses, and many elephants died. Most of the deaths were caused by Alpine avalanches.
  • Where: United States
  • When: 1910
  • The worst snowslide in U.S. history occurred in the Cascade Mountains in Wellington, Washington, when 96 people were trapped when their train became snowbound. An avalanche then swept them to their deaths in a gorge 150 feet below the tracks.
  • Where: Peru
  • When: 1962
  • When tons of ice and snow slid down Huascaran Peak in the Andes Mountains, nearly 4,000 people were killed. Some 30 years later, it is still considered the world's worst avalanche.

For other avalanches, see Floods, Avalanches, and Tidal Waves at Infoplease.com.

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